text input focus: Supports Window::GetFocusedTextInputClient.

ash/root_window_controller.cc

Index: ash/root_window_controller.cc
diff --git a/ash/root_window_controller.cc b/ash/root_window_controller.cc
index 226013f42bdad20ff9f087d9ad5bddaf8bbb9b4a..1e1c5bdaa20937b8e9146734d587308473a3bf39 100644
--- a/ash/root_window_controller.cc
+++ b/ash/root_window_controller.cc
@@ -221,6 +221,7 @@ class EmptyWindowDelegate : public aura::WindowDelegate {
   gfx::Size GetMaximumSize() const override { return gfx::Size(); }
   void OnBoundsChanged(const gfx::Rect& old_bounds,
                        const gfx::Rect& new_bounds) override {}
+  ui::TextInputClient* GetFocusedTextInputClient() override { return nullptr; }
   gfx::NativeCursor GetCursor(const gfx::Point& point) override {
     return gfx::kNullCursor;
   }